A correction:
An intensional fact are those facts that appear in heads of rules (but they
may
also appear in bodies).
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> Behalf Of Agustin Gonzalez
> Sent: Wednesday, June 21, 2000 10:39 AM
> To: [EMAIL PROTECTED]
> Subject: RE: JESS: JESS vs. Prolog
>
>
> Hi Chuck,
> You bring very good points to the table. The need to assert new
> facts comes
> about because the matching algorithm, RETE, needs the new facts, as you
> point out, to figure out if new rules need to fire.
>
> But in a way the comparison is not fair. Because you can get the
> same effect
> as in prolog (display) just by printing "mortal ?x" (again the
> syntax is not
> correct) in the head of the defrule.
>
> However, if you need to use the mortal(?x) fact in other rules you need to
> assert
> it. Similar thing in prolog. If it needed mortal(x) because it's used in
> another rule it would need to create a "temporary" fact to be able to fire
> the rule.
>
> I guess what bothers you, and that's a very good point, is that in RETE
> intensional facts (i.e. those that only appear in heads of rules)
> remain after they are asserted and not removed from the RETE net.
>
> --
> Agustin Gonzalez
> Staff Software Engineer
> LiveMedia, Inc.
> (512) 248-9839
>
>
> > -----Original Message-----
> > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
> > Behalf Of [EMAIL PROTECTED]
> > Sent: Wednesday, June 21, 2000 9:50 AM
> > To: [EMAIL PROTECTED]
> > Subject: JESS: JESS vs. Prolog
> >
> >
> >
> >
> > Please forgive me if this is a misguided missive. I am trying to
> > understand how
> > to use a rule based system, and as such I am sure I am operating
> > under many
> > misunderstandings and misconceptions. I am trying to clear them
> > up, and I would
> > appreciate any corrections to my thoughts below.
> >
> > I have played around a bit with Prolog. As a basic example, I
> > understand if I
> > have these facts and rules:
> >
> > human(Socrates)
> > mortal(X) :- human(X)
> >
> > Then, I can ask the Prolog engine is Socrates mortal by stating
> > "mortal(Socrates)" at the engine prompt, and it will respond with
> > "yes". I can
> > also ask it for all the known mortals with the statement
> > "mortal(X)", and it
> > will respond with "Socrates".
> >
> > I was then thinking how I would do this using Jess. I believe I
> > would use the
> > deffact of
> >
> > (deffact myfacts (human Socrates))
> >
> > and the defrule of
> >
> > (defrule universal-truth ((human ?x) => (assert (mortal ?x))))
> >
> > To find all the mortals, I can define a defquery
> >
> > (defquery all-mortals (mortals ?x))
> >
> > (Sorry, the syntax may be a bit off. I'm not too worried about
> > that. I don't
> > necessarily need responses correcting that. That's easy to fix
> > and understand.
> > It's the concepts that I'm trying to address.)
> >
> > Then, do a (reset) and a (run).
> >
> > Then execute the defquery with the statement
> >
> > (bind ?e (run-query all-mortal))
> >
> > and use an iteration of ?e to get all the results. (The Jess
> > Language manual
> > has an example.)
> >
> > I believe this is the only way to get a similiar functionality to
> > the Prolog
> > query "mortal(X)".
> >
> > If that is true, what troubles me about it is the defrule. It
> > basically adds
> > new facts to the set of facts. What this means to me is if I
> > have a set of 100
> > "human" facts, after I do the (reset), I now have an additional
> > 100 "mortal"
> > facts, doubling the number of facts. And if I have some other
> rule about
> > humans, it would also add another 100 facts.
> >
> > This may be considered a feature (because when the new facts are
> > asserted, it
> > may cause other rules to fire), or it may be just a result of the
> > implementation. But, also, In some ways (from one particular
> > angle of view),
> > these asserted facts can be considered "pollution"
> > 1. They take up space.
> > 2. They take up time to generate.
> > 3. If I remove a human fact, the corresponding mortal fact
> > remains. I have to
> > specifically perform extra steps to get rid of it.
> >
> > In the Prolog implementation, issues 3 is not an issue. There
> > can be a minor
> > argument about whether Prolog has issues 1 and 2, but definitely,
> > Prolog will
> > not multiply the number of facts by the number of rules like Jess does.
> >
> > So is there a way to express relationships between facts (ie if X
> > is human, then
> > X is also mortal) without having the relationship specifically
> > stated as a fact
> > for each candidate of the relationship (ie "(human Socrates)", "(mortal
> > Socrates)", "(human Chuck)", "(mortal Chuck)", etc.)?
> >
> > Chuck Sterbis
> > Senior Programmer/Analyst
> > Denniston & Denniston, Inc.
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
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